Development of flow measuring apparatus for determining low flow performance of resistojet thruster is discussed. Diagram of test equipment is presented. Operation of test equipment is described and numerical relationships are explained

Davis, W. S.

English

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Gas 
.
Vacuum
Gas 
Vacuum 
June 1972	 B72-10289 
NASA TECH BRIEF 
Goddard Space Flight Center	 W 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Flow Equation for Porous Plug and Capillary Tube Flow Restrictors 
L__J The problem: 
Until recently, the relationships predicting the low-
flow performance of resistojet thruster systems were 
nonexistent. The compressible Darcy equation and the 
Greeii and Duwez expression did not adequately describe 
the low-flow characteristics of such systems. 
The solution: 
An empirical model was formulated for both the
porous and capillary elements that describes their low-
flow characteristics. 
How it's done: 
Sets of metal flow restrictors covering two orders of 
magnitude of permeability were flow tested with nitro-
gen, argon, and ammonia gases. Measurements were 
taken using the apparatus shown in the figure. 
(eontinuerf nvrlif) 
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Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
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Fresh test gas is introduced through valve #1 at the 
pressure measured by gage P 1 . With the valve #3 open, 
both the reservoir volume V 1 and the reference volume 
Vf are charged to the same initial pressure. Electron-
ically operated valve #6 separates the test gas from the 
test specimen on the downstream side of the key block. 
Constant pressure downstream is maintained by the surge 
tank V2 and is monitored by gage P 2 . The switch con-
trolling valve #6 is connected to an electronic counter 
which measures the flow duration. From this duration, 
an average flow rate is derived. 
The flow charts generated from the test data suggest 
that the following model is useful for both porous and 
capillary elements: 
.(p1n
T 
where ' is the mass flow rate; T is the absolute tempera-
ture; P 1 and P2 are the absolute upstream and down-
stream pressures, respectively; n is a pressure exponent
indicating the resultant effects of viscous and inertial 
forces; and K is a constant related to the physical charac-
teristics of the restrictor such as area, length, permea-
bility, surface roughness, etc. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: TSP72-10289 
Patent status: 
No patent action is contemplated by NASA. 
Source: W. S. Davis of
Avco Corp.
under contract to
Goddard Space Flight Center
(GSC-1 1387) 
B72-10289	 Category 06


Flow equation for porous plug and capillary tube flow restrictors

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